Venezuela's top opposition leader has asked why President Hugo Chavez has not spoken publicly in more than two months while undergoing cancer treatment in Cuba.

Henrique Capriles questioned the president's long silence at a news conference on Thursday, a day after the vice president provided a new vaguely worded update saying Mr Chavez is undergoing "extremely complex and tough" treatments in Cuba.

Mr Capriles asked why, if a president can sign documents to approve measures such as a newly enacted devaluation, "he's not going to be able to speak to the country".

The opposition leader said that if Mr Chavez does not appear publicly, "then they're lying. Then it isn't true that the president talks and signs. You're forging (his) signature. You're all lying to Venezuelans using the president's signature to justify all the awful things you're doing."

The 58-year-old president underwent surgery on December 11 for an undisclosed type of pelvic cancer. Since then, the government has provided regular updates, though there have been fewer updates in recent weeks.

Officials including Vice President Nicolas Maduro and others have travelled repeatedly to Havana, and Mr Maduro has shown documents signed by Mr Chavez on television.

The leader's two-month silence has fed speculation about why Mr Chavez would be incapable of speaking by phone on television, as he has during past treatments. Mr Chavez has had tumours repeatedly removed from his pelvic region, and has also undergone prior rounds of chemotherapy and radiation treatment.

Medical experts consulted by The Associated Press have said the government's recent account of "systemic medical treatment" could mean various types of chemotherapy or drug treatments, depending on the type of cancer.

Speaking to reporters on Thursday, Mr Capriles also condemned the latest currency devaluation, saying the government now should raise the minimum wage to compensate working-class Venezuelans as the country struggles with 22% inflation.

"The whole country, we're going to get organised to put the brakes on this package," Mr Capriles said, referring to the economic measures. He said only the government benefits from the devaluation by turning its dollar-denominated oil earnings into larger sums of local currency, but that regular citizens suffer.

Mr Maduro rebuffed Mr Capriles' criticisms saying the governor should get back to work in his own state. The vice president also said Mr Capriles seems "obsessed" with being a presidential candidate again. Mr Capriles lost to Mr Chavez in the country's October presidential election.